1. Field of the Invention
The present invention relates to a method for recovering the heat of vaporization of the methanol recovery section of a methyl tertiary butyl ether (MTBE) plant.
2. Related Art
The production of methyl tertiary butyl ether (MTBE) is usually carried out by selectively reacting isobutene contained in a refinery C.sub.4 stream with methanol in the presence of an acid catalyst. The resulting MTBE product is separated from the C.sub.4 stream which is then potentially useful for other purposes such as alkylation.
The separation of MTBE from the hydrocarbon product stream is not a problem because of the boiling point difference between MTBE and C.sub.4, the DME and methanol are lower boiling and contaminate the C.sub.4 fraction.
The recovery and recycle of unreacted methanol is essential to the economics of the overall conventional MTBE process. Notwithstanding the particular MTBE reaction system used for the direct reaction of methanol with isobutene in mixed C.sub.4 streams, it may be necessary to employ a water wash to separate methanol from the unreacted C.sub.4, since the C.sub.4 's form azeotropes with methanol and a clean separation cannot be obtained by distillation alone.
The removal of methanol from the C.sub.4 's can be carried out with a water wash system, since methanol is relatively soluble in water, and the methanol can be readily separated by distillation from the water, which is a conventional procedure. The problem is the loss of energy required to distill the methanol. The distillation of methanol from the wash water is presently conducted at low pressure. Under the usual pressure conditions the methanol overhead condenses at around 65.degree. to 71.degree. C.